1. Field of the Invention
The present invention relates to a display device, a gray scale processing circuit, and a method of gray scale processing, for performing gray scale processing to display an image on a display panel such as a liquid crystal panel.
2. Description of the Related Art
In display devices for displaying images on a display panel, the brightness levels which the display panel can display, i.e., the display brightness levels, are prescribed at certain intervals corresponding to the brightness levels of input image data for each pixel. The display brightness level is defined at intervals of one level, for example, starting from a brightness level of 0 followed by 1, 2, 3, . . . Suppose the brightness level of image data to be desired to display includes a decimal fraction, for example, a brightness level 0.50 of the image data. In this case, gray scale processing is carried out such that the frames of brightness levels 0 and 1 are alternately displayed for a certain period of time to create a brightness level of 0.50 in a pseudo manner. In the gray scale processing, for example, a slightly lower display brightness level than a desired brightness level and a slightly higher display brightness level are repeatedly displayed at such a high speed that human eyes cannot follow the repetitions. In this manner, the desired brightness level of the image data is recognized by a viewer.
As shown in FIG. 1 of the accompanying drawings, a display device for gray scale processing includes a gray scale processing circuit. The gray scale processing circuit has a gray scale pattern generator circuit 1 and an adder 2. The gray scale processing circuit is supplied with input image data of eight bits indicative of a brightness level. The lower two bits of the 8-bit input image data are equivalent to the decimal places of the brightness level and supplied to the gray scale pattern generator circuit 1, and the upper six bits are supplied to the adder 2. The gray scale pattern generator circuit 1 uses the lower two bits corresponding to the brightness level of the decimal places as a gray scale level, so as to produce one-bit gray scale pattern data according to the gray scale level. The adder 2 adds the one-bit gray scale pattern data to the lowest bit of the 6-bit data and then sends the resulting 6-bit image data to a source driver (not shown).
FIG. 2A to FIG. 2C of the accompanying drawings shows the gray scale pattern data of the gray scale levels of 0.25 (the lower two bits=“01”), 0.50 (the lower two bits=“10”), and 0.75 (the lower two bits=“11”) in the gray scale pattern generator circuit 1, respectively. Specifically, the gray scale pattern data for a gray scale level of 0.25 is indicative of 0, 1, 0, 0 in the respective frames; the gray scale pattern data for a gray scale level of 0.50 is indicative of 0, 1, 0, 1 in the respective frames; and the gray scale pattern data for a gray scale level of 0.75 is indicative of 0, 1, 1, 1 in the respective frames. The gray scale pattern data is made up of four frames, and repeatedly used.
Suppose pixel data is indicative of a brightness level, for example, 1.75. This brightness level is occasionally referred to as “desired brightness level.” An immediately lower display brightness level of 1 than the desired brightness level (i.e., brightness level of 1.75) and an immediately higher display brightness level of 2 are used as shown in FIG. 3 of the accompanying drawings. Specifically, the brightness levels of the display panel are controlled in four frames so as to become as the lower display brightness level 1, the higher display brightness level 2, the higher display brightness level 2, and the higher display brightness level 2 in the four frames, respectively.